Recently, Flash memory (Flash EEPROM) is used in various kinds of electronic devices including portable devices, such as, digital cameras and smartphones. Flash memory is, for example, a memory (a storage medium, a secondary storage) that takes longer erasure time than data read time and that erases all data before sequentially writing data to a write region.
Meanwhile, for example, a computer (CPU) manages data on a memory in units of files/directories using a FAT (File Allocation Table) file system.
For example, Flash memory such as an SD card (an SD memory card) that is used with a digital camera or a portable device, adopts a FAT file system, whereby the memory (SD card) region is efficiently allocated to files of various different sizes.
As described above, Flash memory such as an SD card that is used with a digital camera or a portable device adopts a FAT file system, whereby the region of the SD card is efficiently allocated to files with various different sizes.
Recently, the storage capacity of Flash memory such as an SD card has remarkably increased with margin so ample that one hardly feels shortage of the capacity. However, for example, write processing to an SD card is often clearly distinguished between cases where write time is long and short.
When write time is long, for example, the write time may take approximately 100 times as long as write time when the write time is short, which is attributable to whether erasure operation of Flash memory occurs inside the SD card upon writing.
In other words, in Flash memory such as an SD card or the like, rewriting from data “1” to data “0” can be carried out as is, while erasure operation is involved for rewriting from data “0” to data “1”.
Since the erasure operation takes long time, a large time difference is generated between time that is taken for rewrite processing without erasure operation and time that is taken for rewrite processing with erasure operation. As such, varied write time to a memory causes extension of the completion time of writing a file.
Incidentally, in the past, various proposals have been made for a method of managing a memory (a storage medium, a secondary storage) or a technique of controlling a memory relating to a FAT file system.
Patent Document 1: Japanese Laid-open Patent Publication No. 2006-318366
Patent Document 2: Japanese Laid-open Utility Model Publication No. 2008-117491
Patent Document 3: Japanese Laid-open Patent Publication No. 2009-258921
Patent Document 4: Japanese Laid-open Utility Model Publication No. 2004-213746